I. Field of the Invention
This invention relates generally to fire fighting apparatus, and more particularly to a system for introducing a liquid foam concentrate into a water stream in varying amounts to maintain a predetermined percentage mixture, irrespective of variations in the flow rate of the water stream where the system is automatically conditioned upon application of electrical power.
II. Discussion of the Prior Art
In our earlier U.S. Pat. No. Re. 35,362, the contents are which are hereby incorporated by reference, as if set out in full herein, there is described a system for controlling the introduction of a liquid chemical foamant into a water stream used in fighting fires at an appropriate flow rate so that the amount of foam in the water stream is of a predetermined concentration, irrespective of variations in the water flow rate. Identified in the '362 patent as an “optional enhancement” is the inclusion of a compressed air source for projecting the foam/water mixture a greater distance as it exits a hose or water cannon. As described therein, it is important that the compressed air not be introduced into the water stream in the absence of the foam additive. Upon arriving at a fire, a human operator must start the introduction of the liquid chemical foamant by depressing an “on/off” switch on the controller module. As is explained in the '362 patent, upon depression of the on/off push button 32, the microprocessor in the controller module 26 executes an algorithm represented by the flow chart of FIG. 9 of that patent to control the introduction of foam concentrate into a water stream being pumped whereby the percentage concentration is maintained relatively constant irrespective of variations in the water flow rate as the fire fighter manipulates a hose nozzle.
It has been found advantageous to eliminate the need for a human operator to initiate operation. If either due to inattention or the excitement of the moment, a fire fighter should fail to depress the start button, air may be introduced in the water stream without the foam additive. Accordingly, it is a principal purpose of the present invention to provide a control feature that will assure that the system is in an auto-start condition at the time power is applied, obviating the need for a human operator to turn on the foam control system. The improvement to the prior art foam injection system described herein reduces the time needed to activate the foam injection system while providing all of the necessary safety interlocks to prevent untimely activation. Moreover, by implementing the present invention, only a single switch is needed in the cab of a fire-fighting vehicle thereby facilitating “pump & roll” operation of the vehicle when creating a fire brake when dealing with grass and brush fires.